我的Design Pattern之旅[4]：使用Generic改進Strategy Pattern(OO)

Abstract

在(原创) 我的Design Pattern之旅：使用template改进Strategy Pattern (OO) (Design Pattern) (C/C++) (template)中，使用了C++的template改进strategy pattern，本文使用C#的generic改进strategy pattern。

Introduction

C# 2.0加入了generic对泛型的支援，所以想将原来C++的template程式一行一行的改成C# generic。

在strategy pattern中，通常为了让strategy能完全存取物件的public method/property，我们会利用传this将整个物件传给strategy

public void drawShape() {
　this.shape.draw(this);
}

为了达成此需求，我们的interface须如此定义

interface IShape {
　void draw(Grapher grapher);
}

完整的程式码如下

1/**//*
2(C) OOMusou 2007 http://oomusou.cnblogs.com
3
4Filename　　: DP_StrategyPattern3_polymorphism_this.cs
5Compiler　　: Visual Studio 2005 / C# 2.0
6Description : Demo how to use Strategy Pattern with this
7Release　　 : 04/07/2007 1.0
8*/
9using System;
10
11interface IShape {
12　void draw(Grapher grapher);
13}
14
15class Grapher {
16　private IShape shape;
17　private string text;
18
19　public Grapher() { }
20　public Grapher(IShape shape) : this(shape, "Hello Shape!!") { }
21　public Grapher(IShape shape, string text) {
22　　this.shape = shape;
23　　this.text = text;
24　}
25
26　public void drawShape() {
27　　this.shape.draw(this);
28　}
29
30　public void setShape(IShape shape, string text) {
31　　this.text = text;
32　　this.shape = shape;
33　}
34
35　public string getText () {
36　　return this.text;
37　}
38}
39
40
41class Triangle : IShape {
42　public void draw(Grapher grapher) {
43　　Console.WriteLine("Draw {0:s} in Triangle", grapher.getText());
44　}
45}
46
47class Circle: IShape {
48　public void draw(Grapher grapher) {
49　　Console.WriteLine("Draw {0:s} in Circle", grapher.getText());
50　}
51}
52
53class Square : IShape {
54　public void draw(Grapher grapher) {
55　　Console.WriteLine("Draw {0:s} in Square", grapher.getText());
56　}
57}
58
59class main {
60　public static void Main() {
61　　Grapher theGrapher = new Grapher(new Square());
62　　theGrapher.drawShape();
63
64　　theGrapher.setShape(new Circle(), "Hello C#!!");
65　　theGrapher.drawShape();
66　}
67}

执行结果

Draw Hello Shape!! in Square
Draw Hello C#!! in Circle